Tuesday, November 14, 2006 - 2:00 PM

Role of Dissolved Organic Nitrogen in Agroecosystem Sustainability.

Davey L. Jones, Paula Roberts, John Farrar, and Paul Hill. Univ of Wales Bangor, School of Agricultural and Forest Sciences, Deiniol Road, Bangor, United Kingdom

The availability of inorganic N has been shown to be one of the major factors limiting primary productivity in polar ecosystems. The factors regulating the rate of transformation of organic N to nitrate and ammonium, however, remain poorly understood. Further, recent evidence has suggested that DON in the form of amino acids represents a readily available source of nitrogen and carbon for both plants and soil microorganisms. In the case of plants, both mycorrhizal and non-mycorrhizal roots, from a broad range of ecosystem types, appear to possess the capability to take up significant quantities of proteinaceous amino acids. The importance of this inwardly directed DON flux in comparison to NO3- and NH4+ (DIN) remains unknown. The aim of this research was therefore to quantify and characterise the DIN and DON pools in a range of temperate and polar soils and to calculate the flux through these pools. Generally, the DON pool was much larger than the DIN pool, however, most of this DON was of high molecular weight (MW) and relatively recalcitrant. The low MW pool in the form of amino acids was similar in size to the DIN pool which was frequently dominated by NH4+. Incubations of low MW DON with soil indicated a rapid processing of amino acids, di- and tri-peptides to NH4+ followed by a slower transformation of the NH4+ pool to NO3-. The rate of protein transformation to NH4+ was slower than for amino acids and peptides suggesting that the block in N mineralization in polar soils is the transformation of high MW DON to low MW DON and not low MW DON to NH4+ or NH4+ to NO3-. We will present evidence to show the context specific nature of plant-microbial competition for N resources in soil.